advent-of-code/2023/day18.py

import sys
from typing import Literal, TypeAlias, cast

Direction: TypeAlias = Literal["R", "L", "U", "D"]

DIRECTIONS: list[Direction] = ["R", "D", "L", "U"]
MOVES: dict[Direction, tuple[int, int]] = {
    "R": (0, +1),
    "L": (0, -1),
    "U": (-1, 0),
    "D": (+1, 0),
}


def area(corners: list[tuple[int, int]], perimeter: int) -> int:
    area = abs(
        sum(c0[0] * c1[1] - c0[1] * c1[0] for c0, c1 in zip(corners, corners[1::])) // 2
    )
    return 1 + area - perimeter // 2 + perimeter


def polygon(values: list[tuple[Direction, int]]) -> tuple[list[tuple[int, int]], int]:
    perimeter = 0
    corners: list[tuple[int, int]] = [(0, 0)]
    for direction, amount in values:
        perimeter += amount
        corners.append(
            (
                corners[-1][0] + amount * MOVES[direction][0],
                corners[-1][1] + amount * MOVES[direction][1],
            )
        )
    return corners, perimeter


lines = sys.stdin.read().splitlines()


# part 1
answer_1 = area(
    *polygon([(cast(Direction, (p := line.split())[0]), int(p[1])) for line in lines])
)
print(f"answer 1 is {answer_1}")

# part 2
answer_2 = area(
    *polygon(
        [
            (DIRECTIONS[int((p := line.split()[-1])[-2])], int(p[2:-2], 16))
            for line in lines
        ]
    )
)
print(f"answer 2 is {answer_2}")